International Association for Cryptologic Research

# IACR News Central

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Further sources to find out about changes are CryptoDB, ePrint RSS, ePrint Web, Event calender (iCal).

2015-06-02
09:17 [Pub][ePrint]

Profiled side-channel attacks are understood to be powerful when applicable: in the best case when an adversary can comprehensively characterise the leakage, the resulting model leads to attacks requiring a minimal number of leakage traces for success. Such complete\' leakage models are designed to capture the scale, location and shape of the profiling traces, so that any deviation between these and the attack traces potentially produces a mismatch which renders the model unfit for purpose. This severely limits the applicability of profiled attacks in practice and so poses an interesting research challenge: how can we design profiled distinguishers that can tolerate (some) differences between profiling and attack traces?

This submission is the first to tackle the problem head on: we propose distinguishers (utilising unsupervised machine learning methods, but also a down-to-earth\' method combining mean traces and PCA) and evaluate their behaviour across an extensive set of distortions that we apply to representative trace data. Our results show that the profiled distinguishers are effective and robust to distortions to a surprising extent.

06:17 [Pub][ePrint]

Securely sharing the same secret key among multiple parties

is the main concern in symmetric cryptography that is the workhorse

of modern cryptography due to its simplicity and fast speed. Typically asymmetric cryptography is used to set up a shared secret between parties, after which the switch to symmetric cryptography can be made. In this paper, we introduce a novel key exchange protocol based on physical hardware implementation to establish a shared secret between parties rather than relying on mathematical implementation of asymmetric cryptography. In particular, the key exchange is dependent on a new security concept named as virtual proof of reality or simply virtual proof (VP) that enables proof of a physical statement over untrusted digital communication channels between two parties (a prover and a verifier) residing in two separate local systems. We firstly exploit the VP to secure key exchange and further prove it by using experimental data. The key transferred in this protocol is only seen by the prover and hidden from not only the adversary but also the verifier. While only the verifier can successfully discover it.

05:07 [Job][New]

The Computer Science department at the University of Auckland seeks 2 Ph.D. Students to join the cloud security team led by Dr. Giovanni Russello.

This research will take place in a new MBIE-funded Cyber Security STRATUS (Security Technologies Returning Accountability, Transparency and User-centric Services to the Cloud) project and will be in collaboration with University of Waikato, UniTech, the Cloud Security Alliance, and several New Zealand-based industrial partners (https://stratus.org.nz). The aim is to research novel yet practical cloud security tools to be adopted by the industry partners.

The research conducted by the University of Auckland’s team will focus on applied cryptography for retrieval and processing of encrypted data in outsourced and untrusted environments. This involves a substantial program of research to develop, implement and apply to industrial case studies.

Applicants are required to have completed (or be close to completing) a Master degree (or equivalent) with outstanding grades in Computer Science, Mathematics, or closely related areas. Additional knowledge in related disciplines such as, e.g., complexity theory or IT security is welcome.

The candidate should be able not only to design but also implement working prototypes of the crypto scheme developed during the research period.

The STRATUS project will provide a stipend of 25,000 NZD p.a. and cover the costs of the tuition fee for 3 years.

05:07 [Job][New]

The Computer Science department at the University of Auckland seeks a Research Fellow/Postdoctoral Researcher to join the cloud security team led by Dr. Giovanni Russello.

This research will take place in a new MBIE-funded Cyber Security STRATUS (Security Technologies Returning Accountability, Transparency and User-centric Services to the Cloud) project and will be in collaboration with University of Waikato, UniTech, the Cloud Security Alliance, and several New Zealand-based industrial partners (https://stratus.org.nz). The aim is to research novel yet practical cloud security tools to be adopted by the industry partners.

The research conducted by the University of Auckland’s team will focus on applied cryptography for retrieval and processing of encrypted data in outsourced and untrusted environments. This involves a substantial program of research to develop, implement and apply to industrial case studies.

This is a full time post for a fixed-term of 2 years. Salary starts at 74000 NZD per annum.

Applicants should have a Ph.D. in computer science in a relevant field (cloud security with emphasis on crypto solutions) a demonstrable research interest in the area of applied crypto with emphasis in homomorphic encryption for encrypted data processing and retrieval focusing on cloud computing, and experience in designing, analysing, and efficiently implement novel crypto algorithms. Previous experience in the area of big data with emphasis on privacy/confidentiality would be advantageous.

2015-06-01
16:05 [Event][New]

Submission: 10 August 2015
From November 1 to November 3
Location: Beijing, China

2015-05-31
21:17 [Pub][ePrint]

In this paper, we present a single round two-party attribute-based authenticated key exchange protocol. Since pairing is a costly operation and the composite order groups must be very large to ensure security, we focus on pairing free protocols in prime order groups. We propose a new protocol that is pairing free, working in prime order group and having tight reduction to Strong Diffie Hellman (SDH) problem under the Attribute-based CK model which is a natural extension of the CK model for the public key setting. Our proposed attribute based authenticated key exchange protocol (ABAKE) also does not depend on any underlying attribute based encryption schemes unlike the previous solutions for ABAKE. Ours is the first scheme that removes this restriction. Thus, the first major advantage is that smaller key sizes are sufficient to achieve comparable security. Our scheme has several other advantages. The major one being the capability to handle active adversaries. Most of the previous Attribute-Based authenticated key exchange protocols can offer security only under passive adversaries. Our protocol recognizes the corruption by an active adversary and aborts the process. In addition to this property, our scheme satisfies other security properties that are not covered by CK model such as forward secrecy, key compromise impersonation attacks and ephemeral key compromise impersonation attacks.

21:17 [Pub][ePrint]

We present a new, decentralized, efficient, and secure digital cryptocurrency, in which the ordinary users themselves keep turns to ensure that the systems works well.

21:17 [Pub][ePrint]

We give a simple heuristic sieving algorithm for the $m$-dimensional

exact shortest vector problem

(SVP) which runs in time $2^{0.3112m +o(m)}$. Unlike previous time-memory

trade-offs, we do not increase the memory, which stays at its bare minimum

$2^{0.2075m +o(m)}$. To achieve this complexity, we borrow a recent tool

from coding theory, known as nearest neighbor search for binary code

words. We simplify its analysis, and show that it can be adapted to solve

this variant of the fixed-radius nearest neighbor search problem:

Given a list of exponentially many unit vectors of $\\mR^m$, and an

angle $\\gamma\\pi$, find all pairs of

vectors whose angle $\\leq\\gamma\\pi$. The complexity is sub-quadratic which leads to the improvement for lattice sieves.

21:17 [Pub][ePrint]

Recently, there has been huge progress in the field of concretely efficient secure computation, even while providing security in the presence of malicious adversaries. This is especially the case in the two-party setting, where constant-round protocols exist that remain fast even over slow networks. However, in the multi-party setting, all concretely efficient fully-secure protocols, such as SPDZ, require many rounds of communication.

In this paper, we present an MPC protocol that is fully-secure in the presence of malicious adversaries and for any number of corrupted parties. Our construction is based on the constant-round BMR protocol of Beaver et al., and is the first fully-secure version of that protocol that makes black-box usage of the underlying primitives, and is therefore concretely efficient.

Our protocol includes an online phase that is extremely fast and mainly consists of each party locally evaluating a garbled circuit. For the offline phase we present both a generic construction (using any underlying MPC protocol), and a highly efficient instantiation based on the SPDZ protocol. Our estimates show the protocol to be considerably more efficient than previous fully-secure multi-party protocols.

2015-05-30
09:17 [Pub][ePrint]

We provide a formal treatment of security of digital signatures against *subversion attacks* (SAs).

Our model of subversion generalizes previous work in several directions, and is inspired by the proliferation of software attacks (e.g.,\\ malware and buffer overflow attacks), and by the recent revelations of Edward Snowden about intelligence agencies trying to surreptitiously sabotage cryptographic algorithms.

The main security requirement we put forward demands that a signature scheme should remain unforgeable even in the presence of an attacker applying SAs (within a certain class of allowed attacks) in a fully-adaptive and *continuous* fashion.

Previous notions---e.g.,\\ the notion of security against algorithm-substitution attacks introduced by Bellare et al. (CRYPTO \'14) for symmetric encryption---were non-adaptive and non-continuous.

In this vein, we show both positive and negative results for the goal of constructing subversion-resilient signature schemes.

-Negative results. As our main negative result, we show that a broad class of randomized signature schemes is unavoidably insecure against SAs, even if using just a single bit of randomness.

This improves upon earlier work that was only able to attack schemes with larger randomness space. When designing our new attack we consider undetectability as an explicit adversarial goal, meaning that the end-users (even the ones knowing the signing key) should not be able to detect that the signature scheme was subverted.

-Positive results. We complement the above negative results by showing that signature schemes with *unique* signatures are subversion-resilient against all attacks that meet a basic undetectability requirement. A similar result was shown by Bellare et al. for symmetric encryption, who proved the necessity to rely on *stateful* schemes; in contrast unique signatures are *stateless*, and in fact they are among the fastest and most established digital signatures available.

We finally show that it is possible to devise signature schemes secure against arbitrary tampering with the computation, by making use of an un-tamperable cryptographic reverse firewall (Mironov and Stephens-Davidowitz, EUROCRYPT \'15), i.e., an algorithm that \"sanitizes\" any signature given as input (using only public information). The firewall we design allows to successfully protect so-called re-randomizable signature schemes (which include unique signatures as special case).

As an additional contribution, we extend our model to consider multiple users and show implications and separations among the various notions we introduced.

While our study is mainly theoretical, due to its strong practical motivation, we believe that our results have important implications in practice and might influence the way digital signature schemes are selected or adopted in standards and protocols.

09:17 [Pub][ePrint]

The selfish-mine strategy in Bitcoin allows a miner to gain mining rewards more than her fair share. Prior defenses focus on preventing the attacker from winning a block race of equal-length chains. However, an attacker with more than one third of the computational power can still earn more block rewards even if she loses all equal-length block races. In this work we propose a novel defense mechanism. Our defense requires miners to publish intermediate blocks, or in-blocks for short, blocks that are valid with slightly lower puzzle difficulty, and mine on each others\' in-blocks. When a fork happens, the branch with most total amount of work, rather than the longest chain, will be adopted. Under our scheme, a selfish miner needs to have almost half of the computational power of the network to gain an unfair advantage, thus the selfish-mine strategy is no longer a threat to the system.